Electrical contact



April 10, 1951 1J. D. KLEIS 2,548,164

ELECTRICAL CONTACT Filed Nov. 28, 1947 Conzacz Disc of S2! ver- Germ an /'um I fill oy 4 W 0.05 0./0 0J5 0.20 0.25 Fine PER CENT GERMAN/UM Silver JOHN 0. M95

INVENTOR.

BYA %M Patented Apr. 10, 1951 ELECTRICAL CONTACT 7 John D. Kleis, Lake Forest, 111., assignor to Fansteel Metallurgical Corporation,

North Chicago,

111., a corporationof New York Application November 28, 1947, Serial No. 788,526

2 Claims. (Cl. 75-173) This invention relates to electrical contacts, particularly contacts adapted to replace contacts formed. of fine silver.

Silver is one of the most widely used electrical contact materials because of its high heat conductivity and high electrical conductivity. The rate of oxidation of silver is relatively low as .compared to other materials of high heat and electrical conductivities, and this characteristic also accounts for its wide use in the electrical contact art. The contact resistance of contacts formed of silver remains low because any oxide which may be formed on the contact face is decomposed at relatively low temperatures.

Fine silver as generally employed in the electrical contact art consists of at least 99.9% silver, the balance being principally copper. Many applications require that the contact material operate in or make and break a circuit carrying currents higher than the normal current permissible with fine silver or under mechanical conditions such that welding of the contacts is frequently encountered. Various silver alloys and other alloys and compositions have been employed in such instances.

One of the objects of this invention is to provide electrical contacts having a higher current carrying ability than the usual electrical contacts formed of fine silver.

Another object of this invention is to improve the electrical contact characteristics of fine silver.

Other objects and advantages of this invention will become apparent from a consideration of the description and claims which follow.

Fig. 1 of the drawing illustrates an electrical contact with a disc of silver-germanium alloy.

Fig. 2 of the drawing is a graph illustrating the no weld current for contacts formed of fine silver and contacts made in accordance with the present invention.

The present invention contemplates the production of contacts formed of silver to which has been added a small amount or small proportion of germanium. The silver-germanium alloy for such contacts may be formed of the usual silver of commerse which contains small amounts of other elements or metals. The alloy may be formed in any desired manner. A convenient method for the formation of this alloy consists in forming a pre-alloy consisting of relatively large amounts or proportions of germanium. The desired silver-germanium alloy for use in forming the contacts may then be produced by adding an amount of the pro-alloy sufficient to 2 produce a final alloy havingthe desired composition. vThe alloy may also be made by powder metallurgy methods.

I have discovered that electrical contacts formed of silver and fine silver containing up to about 0.25% germanium exhibit superior electrical contact characteristics as compared to those formedof fine silver. The preferred alloy for electrical contact purposes contains from about 0.06% to about 0.23% germanium.

Electrical contacts may be formed of these alloys by any desired method such as melting and casting, punching disks from sheets or by forming the contacts from rod or wire.

The graph illustrates diagrammatically the substantial improvement in the electrical contact characteristics obtained by the addition of these small amounts of germanium to fine silver. The no weld current for electrical contacts is obtained by placing the contacts in an electrical circuit including a resistive load and making and a breaking the circuit 100,000 cycles. The number of welds for a pair of contacts of a single material or alloy is noted while the current is maintained constant for this number of cycles. Additional tests are conducted at other currents in like manner. The number of welds obtained in the different tests are plotted against the current flowing in the circuit. The no weld current is obtained by interpolating the curve for each material to extend the curve to zero number of welds. The point at which the curve intersects the zero weld line indicates the maximum current which contacts formed of that particular material or alloy may carry without a welding and sticking of the contacts in 100,000 cycles. I

From a series of such experimental tests the following results were obtained:

Contact Material 3glg l lmperes Fine Silver 24 Fine Silver+0.065% Ge 28 Fine Silver+0.l0% Gc 32. 5

Fine Silver+0.20% Ge Fine Silver+0.23+ Ge.-- Fine Silvcr+l.0% Ge 0.17%. The current carrying ability then decreases very rapidly so that the no weld current for contacts formed of fine silver containing approximately 0.25% is substantially the same as that for contacts formed of fine silver. Further additions of germanium decrease the current carrying ability.

The addition of the small amounts of germanium as contemplated by the present invention does not adversely affect the contact resistance nor the conductivity of the silver. The presence of the germanium does decrease somewhat the resistance of the silver to tarnishing and oxidation. It has also been discovered that the presence of these small amounts of ger manium reduce the transfer of the contact material.

Contacts formed of silver alloys containing small amounts of other metals are also improved by the addition of the small amounts of germanium contemplated by the present invention.

1. An electrical contact formed of an alloy composed of fine silver and germanium, the germanium constituting up to 0.23% of the alloy, the contact being characterized by having a no weld current characteristic in excess of the no weld current characteristic of contacts formed of fine silver.

2. An electrical contact formed of an alloy composed of fine silver and germanium, the germanium constituting from 0.06% to 0.23% 01' the alloy.

JOHN D. KLEIS.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,154,068 Ellis Apr. 11, 1939 2,221,285 Hensel et al Nov. 12, 1940 FOREIGN PATENTS Number Country Date 681,980 Germany Oct. 4, 1939 OTHER REFERENCES 

1. AN ELECTRICAL CONTACT FORMED OF AN ALLOY COMPOSED OF FINE SILVER AND GERMANIUM, THE GERMANIUM CONSTITUTING UP TO 0.23% OF THE ALLOY, THE CONTACT BEING CHARACTERIZED BY HAVING A "NO WELD" CURRENT CHARACTERISTIC IN EXCESS OF THE "NO WELD" CURRENT CHARACTERISTIC OF CONTACTS FORMED OF FINE SILVER. 